1. Field of the Invention
The present invention relates to a progressive metallic mold apparatus for production of laminated iron cores which has two functions, that is, a skewing function for the purpose of forming slant or skew slots in a laminated iron core and a rotation-laminating function (hereafter called index function) for the purpose of removing unfavorable irregularities in the thickness of the respective iron core sheets or pieces.
2. Description of the Prior Art
There is well known a progressive metallic mold apparatus which has a so-called skewing function for formation of slots in a laminated iron core, for example, as disclosed in U.S. Pat. No. 3,110,831.
In this type of metallic mold apparatus, iron core pieces are made by sequentially blanking a strip material and drawing them into a die by means of a punch and a laminated iron core is obtained by sequentially stacking and calking the drawn core pieces within the die.
Meanwhile, the thickness of the strip material is not uniform due to the inherent strain of a roller used in its rolling operation of the strip production. Accordingly, the core pieces made of the strip material have also an uneven thickness with one side being always thicker than the other. The respective iron core pieces drawn into the die are stacked as mutually shifted by a skew angle but with substantially the same attitude. Therefore, these core pieces have the above-mentioned directional property in the thickness, and thus the resultant laminated iron core made out of such pieces may be inclined as shown in FIG. 11, depending on the degree of the piece's irregularity.
Such a disadvantage can be prevented by a socalled indexing operation, that is, by rotating the die by an angle of 90.degree. or 180.degree. just prior to the blanking of the strip material. However, this requires a large-sized and complicated apparatus and thus there has not been suggested so far a metallic mold apparatus which can have such an indexing function and the earlier-mentioned skewing function.